1. Field of the Invention
The present invention relates to a mask and a film formation method using the mask.
2. Background Art
In recent years, in view of efficient use of energy, solar cells are more widely used than ever before.
As solar cells, a silicon based solar cell such as a silicon solar cell employing single-crystalline silicon, a polysilicon solar cell employing polysilicon layer, an amorphous silicon solar cell employing an amorphous silicon, and the like are known.
A silicon-series solar cell is constituted of a photoelectric converter in which, for example, a transparent electrode which serves as a top-face electrode and which is formed on a glass substrate and composed of TCO (transparent conductive oxide) or the like, a semiconductor layer (photoelectric conversion layer) which is formed on the top-face electrode and composed of silicon, and an Ag thin film which is formed as a back-face electrode are stacked in layers.
The semiconductor layer has a layered structure which is referred to as pin-junction in which a silicon film (i-type) is sandwiched between p-type and n-type silicon films, the silicon film (i-type) generating electrons and holes when receiving light.
Meanwhile, in the above-described solar cell, after the top-face electrode, the semiconductor layer, and the back-face electrode are stacked on the substrate in layers, the photoelectric converter is sealed using a sheet or the like having an insulation property, and a solar cell module is thereby formed.
Since a peripheral portion of the substrate serves as a region to which a sheet is adhered, it is necessary to ensure the adherence property or the sealing characteristics between the solar cell and the sheet, and it is preferable that the photoelectric converter be removed from the peripheral portion of the substrate.
As a method for removing the peripheral portion of the substrate, as shown in, for example, Japanese Unexamined Patent Application, First Publication No. 2007-181904, a method is known in which, after a photoelectric converter is formed over an entire face of substrate, a thin film of the photoelectric converter formed on the peripheral portion is polished and removed by use of a blasting material while protecting the photoelectric converter formed on the portion except for the peripheral portion of the substrate using a mask.
In order to prevent deformation or abrasion which is caused by the blasting material, the mask used in the foregoing method is constituted of a covering component covering the photoelectric converter formed at the region except for the peripheral portion of the substrate and a reinforcing component for increasing the strength of the covering component.
Additionally, as shown, for example, in Japanese Unexamined Patent Application, First Publication No. 2000-133828, a method is known in which a first mask is formed at the peripheral portion of the substrate having translucency where a transparent electrode (top-face electrode) composed of a ZnO film is undesirable to be formed on the peripheral portion of the substrate, a ZnO film is formed using the first mask, and the ZnO film is formed on only the region which is not covered with the first mask.
However, in Japanese Unexamined Patent Application, First Publication No. 2007-181904 described above, when the photoelectric converter which is adhered to the peripheral portion of the substrate is polished using a blasting material, the blasting material is scattered onto a substrate surface or a side face, and there is a problem in that the substrate surface or the side face is damaged.
Furthermore, the blasting material scattered to the inside of the mask, and there is a problem in that the photoelectric converter which is formed on the region other than a removal region is damaged.
If the photoelectric converter is damaged, in order to repair the damaged portion, a process for cleaning the damaged portion, applying a bias voltage to the portion, or the like is necessary in addition to a polishing process using a blasting material.
For this reason, manufacturing efficiency is significantly degraded.
Additionally, in the constitution of Japanese Unexamined Patent Application, First Publication No. 2000-133828, there is a concern that particles of a film forming material scattering in a film forming chamber scatters to the substrate surface or the side face when a film is formed.
When a metal material forming the back-face electrode adheres to, for example, a substrate surface, the transmissivity of sunlight is degraded, and the efficiency of a solar cell is degraded.
In addition, there is a problem in that the particles of the film forming material scattering to the top face side of the substrate are adhered to an inner wall surface of the film forming chamber.
As a result, a maintenance operation of a film forming chamber becomes complicated.